In recent years, following the downsizing of semiconductor devices, the lithography technique (EUVL) using an EUV (Extreme Ultra-Violet) light having a shorter wavelength instead of the conventional ArF laser is considered promising. The EUV light as referred to herein means a light having a wavelength of a soft X-ray region or a vacuum ultraviolet ray region, and specifically, is a light having a wavelength of from about 0.2 to 100 nm. Currently, as a lithography light source, the use of the light having a wavelength in the vicinity of 13.5 nm is mainly investigated.
In addition, following the downsizing of semiconductor devices, a problem of defects on a photomask which is used in the lithography technique has been actualized, In particular, since the photomask is fabricated by subjecting a mask blank to pattern processing, a problem of defects on the mask blank has been actualized.
In order to avoid the problem of defects on the mask blank, there has been developed a technique for identifying a defect position on the mask blank and changing a position or direction of the processing pattern in accordance with the defect position. In addition, in order to identify the defect position on the mask blank, there has been proposed a technique for forming a concave fiducial mark that indicates a fiducial position of the mask blank (see, for example, Patent Document 1).
The mask blank is a multilayer substrate obtained by depositing a multilayer film on a substrate. In the mask blank for EUVL, the multilayer film includes a reflective layer that reflects an EUV light and an absorber layer that absorbs an EUV light in this order from the side of the substrate.
In the conventional methods, the defect position on the substrate is identified while taking a position of a fiducial mark formed on the substrate as a fiducial position. In addition, since the fiducial mark is transferred to the multilayer film to be deposited on the substrate, the defect position of each of functional layers constituting the multilayer film is identified while taking the position of the transferred fiducial mark as a fiducial position (see, for example, Patent Document 2).